In the past inductors have been fabricated using conductive coils with or without high permeability cores such as ferrites, as shown in FIG. 1. The inductor is mounted on a substrate and then mounted on a circuit board according to application desired. Integration of these coils with resistors, capacitors, resistor-capacitor networks, or semiconductor devices have not been achieved. Typically, whenever a coil is used as an inductor, it is mounted as a separate part in series with the integrated circuit to achieve the desired functions.
Inductors fabricated using wound coils inherently provide low resistance for a given inductance value, because of their wire thickness and high inductance due to the use of ferrites or other high permeability materials as the core. The combination of coil inductor with other passive components or integrated circuits consumes space on a printed circuit board and also results in a performance degradation due to the necessary interconnects. While several attempts have been made to integrate inductors with integrated circuits, the process used for doing these integrations is complex and expensive. Such prior art is described in Electromagnetics for Engineers, Steven G. Schwartz, Saunders College Publishing, 1990. FIG. 2 shows a top view of a prior art thin film inductor, which is fabricated on a GaAs or ceramic substrate.
Many modern applications, particularly high frequency applications, lend themselves to the integration of inductors with other passive components such as resistors, capacitors, and semiconductor integrated circuits. The integration necessity stems from cost savings, reliability, performance improvements, and space savings on circuit boards and general miniaturization in height, length, and width.